<h2>DESCRIPTION</h2>

<em>v.patch</em> allows the user to combine any number of
vector maps together to create one composite vector
map. If the table structures are identical, attributes are
transferred to the new table.

<h2>NOTES</h2>

Any vectors that are duplicated among the maps being
patched together (e.g., border lines) will have to be
edited or removed after <em>v.patch</em> is run. Such
editing can be done automatically using
<em><a href="v.clean.html">v.clean</a></em>.
<p>
Lines may need to be snapped with <em><a 
href="v.clean.html">v.clean</a> tool=snap,break,rmdupl</em>.
<p>
Boundaries may need to be cleaned with
<em><a href="v.clean.html">v.clean</a> tool=break,rmdupl,rmsa</em>
repeatedly until the <em>rmsa</em> tool (Remove small angles at nodes)
no longer modifies any boundaries. If vector topology is still not
clean, boundaries may also need to be snapped with
<em><a href="v.clean.html">v.clean</a> tool=snap,break,rmdupl</em>.
<p>
When using the <em>-e</em> flag, <em>v.patch</em> shifts category (cat) 
values in the output so that category numbers from the different input 
maps do not overlap. This shift is applied to both the category values 
of the features and the category values in the attribute tables. Hence, 
there is no need to run <em><a href="v.category.html">v.category</a></em> 
and <em><a href="v.db.update.html">v.db.update</a></em> beforehand.
<p>
When using the <em>-a</em> flag, the user has to make sure that the
features in the different maps added to the output map do not have
overlapping category numbers, unless identical category numbers
reflect identical attributes, otherwise the attributes of the added
maps are lost. To avoid this, the user can use <em>v.category
option=sum</em> to change category values of some of the maps before
patching.

<h2>EXAMPLES</h2>

Patch together two maps with mixed feature types:
<div class="code"><pre>
   v.patch input=geology,streams out=geol_streams
</pre></div>

<br>
Append one map to another:
<div class="code"><pre>
   g.copy vect=roads,transport
   v.patch -a input=railroads output=transport --overwrite
</pre></div>


<h2>SEE ALSO</h2>

<em><a href="v.clean.html">v.clean</a></em>,
<em><a href="v.build.html">v.build</a></em>,
<em><a href="v.select.html">v.select</a></em>,
<em><a href="v.overlay.html">v.overlay</a></em>


<h2>AUTHORS</h2>

Dave Gerdes, U.S.Army Construction Engineering 
Research Laboratory
<br>
Radim Blazek, ITC-Irst, Trento, Italy

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